The present invention relates to a wheel suspension and retraction system, more particularly to a retraction arrangement for an amphibious vehicle capable of powered travel on land and water. The invention has particular, but not exclusive, application for an amphibious vehicle in which a user sits astride the vehicle in the manner of a motorcycle, jet ski, quad bike, or the like.
Amphibious vehicles capable of powered travel on both land and water are known. In a typical arrangement, a prime mover (such as an engine or electric motor) is arranged to provide drive to a marine propulsion unit to propel the vehicle on water and to one or more road wheels for travel on land.
Because of the need to drive a marine propulsion unit and at least one road wheel, the power train of an amphibious vehicle is often more complex than that of a conventional road going vehicle or marine-only craft. This can give rise to difficulties in designing a power train to be accommodated in the limited available space, whilst also ensuring that the weight distribution is satisfactory for both land and marine usage. This problem is particularly acute for smaller “sit-astride” type amphibious vehicles that are similar in form to motorcycles, jet-skis, or quad bikes. Such vehicles tend to have narrower, taller bodywork that makes it difficult to accommodate a conventional amphibious vehicle power train.
The problems associated with amphibious vehicles are not limited to the arrangement of the power train, since the limitations of space also have an impact on other aspects of amphibious vehicle design. For example, the suspension for the road wheels has to be accommodated alongside the power train. This can be a particular problem in the case of an amphibious vehicle in which the road wheels are retractable when the vehicle is being used for marine travel.
U.S. Pat. No. 3,903,831 (Bartlett) is one of many prior art examples of amphibious vehicle wheel retraction arrangements. It uses a single hydraulic ram to retract both of the vehicle's front wheels via a rotatable shaft and a series of linkages and chain drives. The use of a single ram to retract two wheels is attractive; but Bartlett's system has many practical drawbacks. For example, it does not disclose shock absorbers (also known as dampers), and wheel suspension is provided using leaf springs and a single rigid axle. Leaf springs are heavy, bulky, and liable to unpredictable onset of inter-leaf friction, especially as the vehicle ages and corrosion sets in. Furthermore, the live axle design used in U.S. Pat. No. 3,903,831, which is almost extinct in contemporary passenger car production, commits a vehicle builder using Bartlett's design to standards of ride and handling which would be uncompetitive against modem light road vehicles. It should be noted that Bartlett's vehicle is an amphibious motor home; while leaf sprung live axles are still common for heavy vehicles, it is imperative for a smaller vehicle to offer independent wheel springing.
Further examples of retractable suspensions may be seen in U.S. Pat. No. 5,755,173 (Rorabaugh), U.S. Pat. No. 5,590,617 (Aquastrada), U.S. Pat. No. 4,958,584, (Williamson), and U.S. Pat. No. 4,241,686 (Westphalen). U.S. Pat. No. 5,590,617 utilises a dual-piston hydraulic ram as an actuator for retracting a pair of wheels, whereas a lead screw is used in the other cases. In all of these designs, use of a single actuator for pairs of wheels and their associated suspension arrangements is apparently a good way to save money and weight; but it is clear from the cross-sectional views provided in each of these patents that all of these retraction arrangements take up a lot of room in terms of height and width.
There is a need, therefore, for an amphibious vehicle having an improved or alternative arrangement for retraction of the wheels that can be more easily accommodated in a smaller space, particularly, but not exclusively, for a sit-astride type amphibious vehicle.
Japanese patent application JP-63-002712A1 of Ishida describes an amphibious vehicle with retractable wheels. The retractable wheels are arranged in pairs longitudinally, fore and aft, along the vehicle; w. With the wheels of each pair connected to a common rocker member whose rotation can raise or lower the wheels. A separate spring and damper assembly is provided for each wheel. The front wheels are not connected to a common rocker arm, nor are the back wheels. This requires a mechanism which extends along the length of the vehicle, which is difficult to package. It mandates deep and wide bodyside cavities, making occupant access difficult, and would raise the vehicle's center of gravity when compared to a conventional suspension, increasing roll angles on land and on water, and with negative effects on ride motions. Ishida requires this packaging to enable easy connection of each rocker arm to a manually windable handle accessible from the vehicle cabin. The rocker arm of Ishida is a straight member and the wheels of Ishida on retraction pivot about axes running transversely, left to right, across the vehicle. This in turn dictates a suspension geometry of pure leading and trailing arms. This allows negligible camber change on corners, severely limiting roadholding on land. A single suspension arm to a front wheel in particular, may lead to considerable problems with wheel shimmy, and associated unpleasant feedback through the steering system.